REPORT ON THE CRINOIDEA. 55 



only small ones. The arms, however, reach an enormous development, and Quenstedt 

 calculates the total " Krone " to contain not less than five million pieces.' 



In the recent PentacrinidaD the arms are generally well developed in proportion to 

 the stem. This proportion is of course least in young individuals, as shown in 

 Pis. XXXV. and LI., while it is greatest in forms like Pentacrinus mulleri, Pentacriniis 

 maclearanus, Pentacrinus tvyville-fhomnoni, and Pentacrinus alternicirrus (Pis. XIV., 

 XVI., XIX., XXV.). These lead a semi-free existence, owing to the fracture of the stem 

 at a node, as was probably also the ease in Extracrinus hriareus with its large 

 " Krone." 



Among the Comatulidse the vegetative system is reduced to a minimum, as they have 

 no stem in the adult condition. The arms, however, are often very extensively developed, 

 f;ir more so than in any recent Pentacrinidas. The ultimate arms of a Pentacrinus or 

 Metacrinus do not often exceed forty in number ; and they rarely consist of more than 

 one hundred joints, though twenty or thirty more may intervene between the last 

 axiUary and the calyx (Pis. XIV., XVI.; PI. XVIII. fig. 1 ; PI. XIX. fig. 1; PI. XXV.; 

 PI XXVIII. fig. 1; PL XXXI. fig. 1; PL XXXIV. fig. 1; Pis. XXXVIII., XL., XLIL; 

 PL XLIII. fig. 4 ; PL XLIV. fig. 2 ; PL XLV. fig. 1 ; Pis. XLVL, XL VIII. ; PL XLlX. 

 fig. 1 ; PL LII. fig. 1). On the other hand, although there are quantities of ten-armed 

 Comatulse, very many species, especially of Actinometra, have from forty to sixty arms; 

 some, like Actinometra bennetti, and Actinometra schlegeli, eighty or more ; and in a few 

 gigantic types like Actinometra nobilis- there may be over one hundred arms. Further, the 

 number of arm-joints is generally from one hundred and twenty to one hundred and fifty, 

 apart from the syzygies ; while in a large Antedon eschrichti or Actinometra bennetti and 

 in other multiradiate species of the latter genus there may be over two hundred arm-joints. 

 Nearly all of them bear pinnules, which are often very long until quite near the arm ends. 

 But in Metacrinus and also in Pentacrinus, though to a considerably less extent, the 

 development of pinnules stops short some little way from the extremity of the arm ; and its 

 outermost segments bear little stumps of two or three joints only, or may even show no 

 signs of pinnules at all (Pis. XXV., XXVIIL, XXXI., XXXIV., XXXVIIL, XL., XLIL; 

 PL XLIII. fig. 4; Pis. XLIV., XLVL, XLVIIL, XLIX., LL, LIL). 



The same peculiarity is repeated on a smaller scale in the ambulacral plates of the 

 pinnules. Those of Comatulse (when present) are continued almost to the end of the 

 pinnule (PL LIV. fig. 6). But in the Pentacrinidse the last few pinnule joints, some- 

 times even four or six, are totally devoid of any ambulacral plating (PL XV. figs. 7-9 ; 

 PL XVL fig. 2; PL XLL fig. 9; PL XLVIL fig. 10; PL XLIX. fig. 7; PL LII. 

 fig. 5). The same is the case with the extremities of the arms. In fact, both in the 

 persistence of the stalk and of the external basals, and also in the nature of the arms, 



1 Encriniden, p. 292. 



2 



'' The specific formula of this type is— a . 3 . - . 3 . 3 . — • 



